This invention relates generally to systems for ultrasound hyperthermia, and, more particularly, relates to apparatus and methods for delivering ultrasonic energy in hyperthermic treatment of internal cancers and other diseases which respond to temperature elevation.
Production of a controllable level of temperature elevation or hyperthermia at pre-selected locations and volumes of tissue has been found to be of significant therapeutic value in the treatment of patients with cancer or other diseases. Several methods utilizing focused ultrasound to produce such hyperthermia have been described in the art. See, for example, the following publications:
Lele, P. P., 1975, "Hyperthermia by Ultrasound," Proceedings of the International Symposium on Cancer Therapy by Hyperthermia and Radiation, American College of Radiology, Washington, D.C., pp. 168-178;
Lele, P. P., 1981, "An Annular-Focus Ultrasonic Lens for Production of Uniform Hyperthermia in Cancer Therapy", Ultrasound in Medicine and Biology, pp. 191-193;
Lele, P. P., 1983, "Physical Aspects and Clinical Studies with Ultrasonic Hyperthermia," Hyperthermia in Cancer Therapy G. K. Hall and Co, pp. 333-367;
"Phased Arrays for the Induction of Local Hyperthermia," Proceedings of the IEEE 1985 Ultrasonics Symposium;
Lele, P. P., 1986, "Rationale, Technique and Clinical Results with Scanned, Focused Ultrasound (SIMFU) System," IEEE Eighth Annual Conference of the Engineering in Medicine and Biology Society;
Lele, P. P., 1987, "Ultrasound: Synergistic Effects and Application in Cancer Therapy by Hyperthermia," Plenum Publishing Corporation;
Lele, P. P., 1987, "Effects of Ultrasound on Solid' Mammalian Tissues and Tumors In Vivo," Plenum Publishing Corporation; and
Lele, P. P. and J. Goddard, 1987, "Optimizing Insonation Parameters in Therapy Planning for Deep Heating by SIMFU," IEEE Ninth Annual Conference of the Engineering in Medicine and Biology Society.
Further, the following U.S. patents disclose examples of recent developments in the hyperthermia field:
U.S. Pat. No. 4,441,486, Pounds
U.S. Pat. No. 4,549,533, Cain et al
U.S. Pat. No. 4,586,512, Do-huu et al
U.S. Pat. No. 4,622,972, Giebeler, Jr.
The Pounds patent discloses a hyperthermia system including a plurality of transducers mounted in an isospherical configuration. Each transducer is configured so that its compressional mode of vibration is suppressed near the center.
The Cain et al patent discloses ultrasound generating apparatus having a plurality of side-by-side tapered piezoelectric transducer elements. Means are provided for energizing the transducer elements with electrical energy having a frequency which is varied to modulate the ultrasound produced by the transducer elements.
The Do-huu et al patent discloses an emitter which focuses ultrasonic radiation into biological tissues for producing localized heating. The radiation emitter consists of a piezoelectric plate subdivided into annular radiating zones of equal width by a set of concentric circular grooves.
The Giebeler, Jr. patent discloses an ultrasound hyperthermia applicator comprising a plurality of transducers which can be operated in different grouping modes. The beams from these elements can be individually focused according to a spiral or multi-spiral focusing scheme, in an attempt to provide uniform heating, without scanning, of a volume greater than the inherent focal size of the individual transmitter elements.
Additionally, European Patent Application Ser. No. 214,782 of Umemura et al discloses a transducer composed of a plurality of elements divided at least in a circumferential direction. The phases of drive signals may be changed according to the respective positions of the oscillating elements, to form an annular focal zone having a variable radius.
Certain conventional systems for ultrasonically induced hyperthermia utilize one or more mechanically or electromechanically scanned, conically convergent spot-focus beams of ultrasound, produced by radially symmetric, high gain acoustic lenses. Such spot-focus lenses concentrate ultrasonic energy in a small spot in which high peak levels of ultrasound intensity are generated.
When employed in the production of therapeutic hyperthermia, conventional spot-focus beam systems suffer from a number of deficiencies. In particular, peak intensities delivered to the target tissue must be kept below the level at which irreversible damage can result through cavitation or excessive heating. The high gain of spot focus lenses therefore severely restricts the total amount of power which can be delivered to the treatment volume for heating to a safe therapeutic temperature.
Additionally, in conventional spot-focus systems, energy delivery is concentrated within the focal volume, which is generally much smaller than the treatment volume. Sustained and uniform heating of the entire treatment volume therefore requires that the spot-focus beam be moved throughout the treatment volume in closely-spaced trajectories, within a period of approximately 1 to 5 seconds. Conventional spot-focus hyperthermia systems typically cannot provide these scan speeds on a sustained basis, resulting in inadequate and non-uniform heating of the tissues in the treatment volume.
Accordingly, there exists a need for hyperthermia methods and apparatus which permit the delivery of high overall levels of ultrasonic energy while eliminating high peak intensities, and which provide high scan speed and enhanced uniformity of heating throughout the treatment volume.
It is accordingly an object of the invention to provide improved ultrasound hyperthermia apparatus.
It is another object of the invention to provide ultrasound hyperthermia apparatus which delivers high overall levels of ultrasonic energy while eliminating high peak intensities.
It is a further object of the invention to provide ultrasound hyperthermia apparatus which produces uniform heating of the treatment volume.
Other general and specific objects of the invention will in part be obvious and will in part appear hereinafter.